The present invention, in some embodiments thereof, relates to electron spin resonance and, more particularly, but not exclusively, to a resonator suitable for electron spin resonance.
Electron spin resonance (ESR) imaging is a technique for obtaining spatially resolved ESR-based data from samples. ESR-based data is obtained by applying on the sample a static magnetic field, exciting electron spins in the sample by electromagnetic waves, and detecting irradiation created by the electron spins as a result of their excitation.
The spatially resolved ESR-based data can, for example, provide information about chemical structure, elucidate biological functions, enable non-invasive medical diagnosis, and be used to solve material science problems.
In classical ESR detection method, termed “induction detection”, the imaged specimen is placed inside a microwave resonator, and is subjected to a static magnetic field and to microwave radiation. Within the framework of “induction detection”, there are two possible schemes to obtain the ESR-based data, pulsed and continuous wave ESR. In pulsed ESR, a specific set of microwave pulses are induced upon the sample and after a short while the spins in the sample create microwave radiation of their own, termed “echo”, which is detected by the resonator and analyzed. In continuous wave (CW) ESR, the sample is irradiated with a continuous microwave irradiation, and the ESR signal is detected by monitoring the microwave signal reflected from the resonator as a function of the static magnetic field.
Spatial information on the location of the spins that create the ESR signal is obtained through the linear dependence of the frequency of the ESR signal on the intensity of the magnetic field. Specifically, a combination of static and time varying magnetic field gradients are applied across the specimen, such that each point in the specimen is exposed to a magnetic field with different intensity at different times. This way, spins from each point irradiate in a different frequency or with different phase, and the frequency or phase is used to determine the location of the spins that created the signal.
The magnetic field gradients are usually applied with gradient coils. The stronger is the gradient provided by the gradient coils, the better is the spatial resolution of the obtained ESR image.
An imaging device, designed to image a specimen when the specimen is inside the imaging device, is said to have “in-situ geometry”. An imaging device, designed to image a specimen when the specimen is outside the imaging device is said to have “ex-situ geometry”. In the context of induction ESR, a specimen is said to be inside the imaging device if it is inside the smallest convex volume that includes the resonator, the gradient coils, and the static magnetic field source.
U.S. Pat. No. 7,403,008, wherein one of the present inventors is a co-inventor, describes a room-temperature in-situ ESR imaging probe, for biological applications, having a resolution of the order of (1 μm)3.
U.S. Published Application No. 20100001728, own by the same assignee as the present application and being hereby incorporated by reference, discloses an ESR imaging probe which comprises a microwave feed and a resonator. The microwave feed transmits microwave energy to the resonator, and the resonator concentrates ESR signals generated and acquires a signal from 1000 electron spins or less within one hour. The ESR signals are sent to a processor for generating an image of a region of interest outside the resonator.
Additional background art includes International Publication Nos. WO2005/073695 and WO02/21147.